Scientists find three more planets beyond solar system
WASHINGTON (AFP): Astronomers say they have irrefutable evidence of at least three planets beyond our solar system, though they almost certainly are inhospitable to life -- at least as we know it.
The discovery of the three planets -- two of which are three times the mass of Earth and the other about the size of the moon -- was reported last week in Science magazine and has kicked up lively interest among American scientists.
Using radio signals, scientists determined that the new planets are some 1,500 light years away and orbit a whirling, dead sphere called a pulsar that instead of emitting light like our Sun, gives off a barrage of invisible deadly radiation.
"This constitutes irrefutable evidence that the first planetary system around a star other than the sun has been confirmed," astronomer Alexander Wolszczcan of Pennsylvania State University wrote in Science.
The pulsar, known as PSR B1257+12, is believed to have been formed by the collapsed husk of a once massive star that died in a cataclysmic explosion called a supernova about a billion years ago.
The neutron star is extremely dense with a mass of about 1.4 times that of the Sun but with a diameter of no more than 17 kilometers (12 miles). While it does not emit light, it does emit radio waves.
Wolszczcan and Dale Frail, of the National Radio Astronomy Observation in Green Bank, West Virginia detected the presence of suspected planets and in 1992 announced their finding.
But astronomers had heard similar announcements before and in every case the supposed planets had proved either impossible to confirm, turned out to be something else, or was an error.
Radio dish
The scientists used the 305-meter radio dish at the Arecibo observatory in Puerto Rico, the world's largest, to detect variations of plus or minus 0.003 second in the arrival times of the radio pulses.
"This is not a hypothesis any longer," Wolszczcan told The Washington Post. "What I have is the proof that we can indeed say planets have been discovered outside the solar system."
Analyzing variations in the signals, the scientists inferred that two or more objects were exerting a disturbing gravitational influence, causing the pulsar to wobble slightly but regularly.
The two largest planets are between 53 million and 70 million kilometers (33 million and 43 million miles) from the pulsar, and their rotation is between 66.6 and 98.2 days. The smallest celestial body completes its rotation in 25.3 days.
Some of the most skeptical astronomers have been won over.
Stephen Thorsett, a pulsar specialist at the California Institute of Technology in Pasadena, California told The New York Times that the research was "very solid and very exciting."
"I think we're all convinced," he said.